The invention relates to a device for determining the position of an interface between different materials in a tank or container. Such devices may be used, for example, to measure the level of a fluid in a tank.
In particular, the invention relates to a fluid level gauge which is adapted to be used, for example, in storage tanks (for example, on ships or on land), in depots, road tankers, retail stations, etc.
Devices adapted to measure the position of interfaces between two or more different materials are generally known. Generally known fluid level gauges are based upon mechanical measuring principles, for example, a float connected to a level indicator. Another known fluid level gauge has been based upon the well-known capacitance measurement principle. Such capacitive gauges operate as follows.
The capacitive level gauge consists of two means, for example, isolated metal tubes, placed vertically in the fluid in the tank or container, said means forming a capacitance. The fluid fills the space between the said means and serves as a dielectric. The dielectric between the said means influences the capacitance value of the gauge. The influence of a determined dielectric on a capacitance value is known to those skilled in the art and will not be explained in detail. Since the dielectric above the level in the tank or container may be a gas, and the dielectric below the level may be a liquid, it will be clear to those skilled in the art that from a capacitance-measurement the level of this liquid in the tank can be determined.
It is also already known to use a sectionalized capacitive level gauge, comprising a plurality of sections or segments, means for measuring the values of the segment-capacitances and means for deriving information concerning the level in the tank from the measured capacitance-values. Examples of such sectionalized capacitive level gauges are U.S. Pat. Nos. 3,935,739 and 3,010,320.
However, such (sectionalized) capacitive level gauges are less suitable to be used in conductive fluids, for example water. Further, such devices can not be used in multi-phase mixtures, for example mixtures of water, oil and gas. Thus, these known gauges can only be used in determining the position of an interface between fluids which have clearly different dielectric constants.
If the dielectric constants of the different fluids are the same, or nearly the same the position of the said interface can not be determined accurately. These and other limitations and disadvantages of the prior art are overcome by the present invention, and improved apparatus are provided for measuring fluid interfaces.